To provide an under member structure which can properly improve air flow from an engine room to a wheel house during running of a vehicle.

The vehicular under member structure includes: an under member, on which groove parts are formed that have a first part formed approximately along the advancing direction of a vehicle and a second part formed so as to have an inclined angle to the advancing direction of the vehicle at the front side of the vehicle from the first part, and apron seals, which are mounted on the under member so as to be movable along the groove parts of the under member.